EU2 used to be 120 slots and it worked beautifully, it was often 100+ people there and much intenser fights than now.
I never had any lag whatsoever, neither fps nor ping. And that was with my old computer from 3-4 years ago.
But people complained, and now its 80slot.
I think a 120slot siege would work very well on most maps, the old classic maps at least. Some of the newer stuff is kinda small and cramped already.
200 actual players wouldnt work well i think, the maps arent designed for it. Some maps would be impossible to assault.
If we got back portable ladders though, then WOHOOOO it would be awesome.